The present invention relates to hot-rolling of steel pieces such as, for example, slabs, blooms, billets, and semifinished steel bars, and, more particularly, to a method and an apparatus suitable for use in continuous hot-rolling of steel pieces.
A conventional hot-rolling line includes roughing rolls and finishing rolls through which a hot slab from a heating furnace is progressively rolled and formed into a coiled strip of a desired thhickness. A disadvantage of this conventional hot-rolling line resides in the fact that there is a low efficiency of rolling work since the slabs are discontinuously rolled.
To avoid this disadvantage, Japanese Patent Laid-Open Publication No. 22500/1980 discloses a continuous rolling method in which a plurality of slabs of a predetermined length, produced by a continuous casting apparatus, pass through a stationary bonding apparatus which is operative to bond the trailing end of a preceding slab to the leading end of a succeeding slab to form a continuous web which is then continuously rolled through a hot-rolling line.
However, the continuous rolling method proposed in the above mentioned Japanese Publication can not be applied to a practical hot-rolling mill due to the following reasons since the slab entering the hot-rolling mill has a thickness of about 200 mm, with a thickness of the slab being as large as 30 to 60 mm at an inlet side of the finishing rolls. Consequently, it is impossible to bond the opposing ends of such thick slabs by a stationary bonding apparatus.
More particularly, the yield from the continuous casting equipment per strand is equal to approximately 1/4 to 1/3 of the yield from the hot-rolling mill, so that it is necessary to successively feed three to four strands of slabs into the hot-rolling mill. In an actual hot-rolling mill, a plurality of slabs cut in a suitable length are successively fed into the hot-rolling mill in a short period of time however, generally, the rolling of a one piece of slab can be finished in a short time period of about one minute at the longest. Therefore, in order to bond the opposing leading and trailing ends of successive slabs in such a short period of time, it is required that the bonding operation be conducted while the slabs are being moved, which requirement cannot be met by a stationary type bonding apparatus.
While pressure welding represents one possible practical method for bonding successive hot slabs, a disadvantage of pressure welding of slabs by merely pressing the opposing ends of slabs resides in the fact that the operational steps require a long time due to conditions such as the cross-sectional shape, scales and the like.
Japanese Patent Laid-Open Publication No. 59748/1976 proposes another hot-rolling method, wherein the lengthwise leading and trailing ends of each of the successive slabs are sheared in the widthwise direction such that each sheared surface makes a predetermined angle (20.degree. to 85.degree.) to the slab surface. The sheared surfaces are then descaled, and the descaled adjacent ends of successive slabs are then pressed together while the slabs are rolled, whereby the slabs are bonded into a long continuous web. One disadvantage of this known method resides in the fact that it is essential that the shearing of the slab ends is made precisely at a predetermined angle of 20.degree. to 85.degree., which precision shearing is quite difficult to attain during a rolling operation. Consequently the shearing has to be conducted in an off-line operation at the inlet side of a heating furnace. Thus, the shearing of the ends of a running slab with such a high precision of shearing surface angle is extremely difficult to perform. Moreover, according to this method, successive slabs are fed into rolls so that the adjacent ends of the slabs are pressed against each other so that it is difficult to precisely determine factors, such as pressing force and reduction ratio, which are required to precisely bond slabs.
Accordingly, an object of the present invention is to provide a continuous steel hot-rolling method and apparatus which permit bonding of hot steel pieces in a short period of time thereby affording a continuous hot rolling of steel slabs.
According to advantageous features of the invention, a method of continuously hot-rolling steel pieces is proposed which includes the steps of bringing a trailing end of a preceding hot steel piece and a leading end of a hot succeeding steel piece in close proximity to each other while the steel pieces are traveling on an upstream side of the rolling mill, shearing the trailing end portion of the preceding steel piece and the leading end portion of the succeeding steel piece while they are held in close proximity to each other, heating the trailing end of the preceding steel piece and the leading end of the succeeding steel piece to a desired temperature immediately after the shearing, pressing the heated leading end surface of the succeeding steel piece to the heated trailing end surface of the preceding steel piece to bond the steel pieces to form a continuous train of steel pieces, and leading the continuous train of the steel pieces into the rolling mill to thereby enable a continuous rolling of the steel pieces.
According to another feature of the invention, an apparatus for continuously hot-rolling steel pieces is provided which includes steel piece holding means for holding a trailing end of a preceding steel piece and a leading end of a succeeding steel piece during a transporting of the steel pieces, with means for shearing the ends of the steel pieces while the ends are held by the steel piece holding means. Means are provided for heating the sheared trailing end of the preceding steel piece and a sheared leading end of the succeeding steel piece up to a predetermined temperature. Means are also provided for driving at least one of the preceding and following steel pieces in a direction parallel to the path of travel of the steel pieces to press and bond the heated trailing end surface of the preceding steel piece and the heated leading end surface of the succeeding steel piece together. A carrier is disposed on an upstream side of the rolling mill and carries or supports the holding means, shearing means, heating means, and pressing means, with the carrier being movable along a path of travel of the steel pieces.